This invention relates to stall protection for protecting brush type motors in the event of stall or partial stall conditions.
Partial stall and blocked rotor conditions could occur from snow packing or ice blocking the fan of the engine cooling fan module of a vehicle. Also, foreign objects such as a rag, a stick, or wet leaves could block the fan and could create partially blocked rotor conditions. Furthermore, worn bearing (partially ceased) could create the same failure mode. In the event of stall or partial stall conditions, the electric motor, without protection, would draw high current and this can cause thermal failure of the motor. Thus, there is a need to provide improved stall protection for an electric motor.
SUMMARY OF THE INVENTION
An object of the invention is to fulfill the need referred to above. In accordance with the principles of the present invention, this objective is achieved by a method of protecting a brush motor from a stall condition. The method includes the steps of providing a brush motor having power brushes that convey power to windings of the motor, and one sensing brush constructed and arranged to obtain an AC signal indicative of a speed of rotation of an armature of the motor, with the speed of rotation being proportional to a frequency of the AC signal. The motor is powered and the AC signal is obtained with the sensing brush and the speed of rotation of the armature is determined. The determined speed of rotation of the armature is compared with a minimum speed value that is indicative of a stall condition of the motor. If the determined speed of rotation of the armature is below the minimum speed value, power to the motor is disconnected.
In accordance with another aspect of the invention, a system for protecting a motor from a stall condition includes a brush motor having power brushes that convey power to windings of the motor, and one sensing brush constructed and arranged to obtain an AC signal indicative of a speed of rotation of an armature of the motor, with the speed of rotation being proportional to a frequency of the AC signal. A controller is constructed and arranged to compare a speed of rotation obtained by the sensing brush with a minimum speed value that is indicative of a stall condition of the motor. A relay is constructed and arranged to disconnect power to the motor if the speed of rotation obtained by the sensing brush is below the minimum speed value.
Other objects, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification.